In a recent computer system, there is widely used a temporary storage device, such as a cache memory or a local memory, which has a smaller capacity and a higher data transfer rate than those of a main memory, in order to compensate for a difference between a data processing speed of a processor and the data transfer rate of the main memory. The temporary storage device increases substantive data transfer rate in performing access the main memory and improve efficiency in data processing by the processor.
However, the temporary storage device is not capable of storing all of the data on the main memory. For this reason, it is necessary to replace the data stored in the temporary storage device with necessary data in accordance with a data access by the processor. However, in some cases, when data to be accessed in the near future by the processor are stored in the temporary storage device, the data may be replaced with other data in accordance with the data access by the processor. When this replacement occurs, the replaced data need to be re-read from the main memory when the processor needs to access the replaced data.
Therefore, there is proposed a technique for prohibiting the replacement of the data stored in a specific area of the temporary storage device. An example of such technique is disclosed in JP-A-2001-290705 (also published as U.S. Pat. Nos. 6,859,862 B1, 6,681,296 B2, and US 2002/0062424 A1).
In the technique disclosed in the document JP-A-2001-290705, it is necessary to determine whether or not the data to be accessed is stored on the temporary storage device every time the processor requests to access the temporary storage device.